This invention relates to welding methods and to novel backup equipment for use therein; the invention is particularly concerned with a novel pressure-sensitive adhesive tape for use in backing up abutted metal strips during formation of a weld.
In the manufacture of large tanks, ships, etc., plates are often joined together by abutting their edges and joining them with a welded seam. It is highly desirable, if not absolutely essential, that there be a complete penetration from face to root of the weld material. In order to permit welding from one side of the abutted plates, it has been common practice to employ metal back-up bars, which may be surfaced with glass cloth or other refractory material to prevent inadvertently joining the backup bar to the weld.
It has also been common, in recent years, to employ heat-resistant tapes, such as glass fabric tapes, either alone or in combination with a further backing such as a metal or ceramic ply. Another extremely popular welding backup tape incorporates a flexible backing coated with adhesive, a strip of flexible refractory particles being adhered to a central portion of the coated side of the backing; such a tape is then adhered to the portions of the plates to be welded which are immediately adjacent to the plane of abutment.
While both backup bars and flexible backup tapes have been used effectively in industry, certain types of welding situations continue to plague the welders. For example, where the parts to be joined have irregular edges and hence vary in gap, or where the current flow to the arc welder tends to fluctuate, localized overheating is likely to occur. In such circumstances, it frequently happens that the refractory material fuses completely and permits a channel of the molten weld metal to flow through. Where a backup bar is employed, such an occurrence may cause the bar itself to become welded to the joint, necessitating inconvenient, expensive, and time-consuming effort to separate it therefrom. On the other hand, where flexible backup tape is employed, burning through the backing may cause the development of an irregular weld which must be ground down after the welding process is completed. This procedure, too, is extremely expensive and inconvenient.
Welding conditions of the type just described are particularly common where large plates or other parts are to be welded together, as occurs in the construction of large storage tanks, units of a ship, etc. Since such equipment is extremely costly, and since it will be subjected to severe operating conditions, it is important that uniform and structurally sound welds be obtained. Prior to the present invention, however, no means was recognized for achieving this objective.